This application claims priority of Japanese Application No. 2000-193658 filed Jun. 28, 2000, the complete disclosure of which is hereby incorporated by reference.
This invention relates to a flexible aromatic polyimide foam having a high glass transition temperature.
Foamed products such as polystyrene foam and polyoelfin foam are well known. These foamed products are rigid and have low heat resistance.
Polyurethane foam is also well known as a flexible foam but also has low heat resistance.
U.S. Pat. No. 4,241,193 discloses dense, rigid polyimide foam which is derived from mixtures of aromatic diamines and partial esters of a benzophenonetetracarboxylic acid.
European Patent Specification (EP) 0 437 821 B1 describes a method for producing polyimide products from a combination of an alkyl ester of a tetracarboxylic acid with at least one aromatic and/or heterocyclic aromatic primary diamine.
A polyimide foam product (tradename: SOLIMIDE) is commercially available from INSPEC Corp. This polyimide foam has a glass transition temperature of approx. 250xc2x0 C.
It is an object of the invention to provide a flexible polyimide foam having a high glass transition temperature.
The invention resides in a flexible aromatic polyimide foam having an apparent density of 70 kg/m3 or less and a glass transition temperature of 300xc2x0 C. or higher.
The flexible aromatic polyimide foam of the invention can be prepared by a process comprising the steps of:
mixing an aromatic tetracarboxylic acid comprising 2,3,3xe2x80x2,4xe2x80x2-biphenyltetracarboxylic dianhydride a portion of which is converted into a mono- or di-lower primary alcohol ester thereof with an aromatic polyamine containing diaminodisiloxane in an amount of 0.1 to 10 mol. %, based on the amount of total amine compounds, to give a solid of polyimide precursor; and
heating the solid of polyimide precursor to a temperature of 300xc2x0 C. to 500xc2x0 C.